A slurry is a liquid mixture, typically comprised of water and soluble and insoluble solid materials. Without agitation, a slurry will separate over time with the solid and liquid attaining distinct levels in a container. Separation in some instances is undesirable. That is, homogenizing a slurry may have various advantages for different fields. For example:                (1) animal manure management, a homogenous slurry is much easier to pump reliably, particularly in screening systems where manure is pumped over a screen to separate into liquid and solid components;        (2) wastewater treatment, a homogenous wastewater slurry in a treatment plant benefits the biological breakdown of human waste. Likewise, in aerobic digestion, oxygen can be added and mixed into a wastewater slurry to facilitate digestion;        (3) food processing such as wine making, a homogenous slurry of grape skins with wine during fermentation can improve the taste of the wine;        (4) bio-waste management (i.e., fats, oils, and greases combined with commercial and household food waste and possibly with animal manure to generate biogas) a homogenous slurry can help improve various stages of the process; and        (5) manufacture of fuels, such as fuel oils, bio-diesel and ethanol, a homogenous slurry can be helpful in improving the process.Accordingly, mixers have been used to create and maintain homogeneity in slurries.        
The first of such mixers were used on farms and the like to mix manure pits and lagoons. This early portable mixer was typically mounted on and driven by a tractor. Later, belt-driven AC electric motor mixers came about for use in large tanks. However, these open impeller systems only worked well when slurry level was high in the tank. Low slurry levels resulted in vortexing and diminished mixing effectiveness. Further, materials such as hair, fabrics, sludge and the like tended to wrap around the impeller and impeller shaft causing seal failures and leading to high maintenance expenses.
A system was needed to address the problems of low slurry levels and string-like solids. A system which could operate effectively at slurry levels below four feet, and even down to a foot of slurry was sought by those of skill in the art. A system which could reduce the impact of wrapping solids to minimize maintenance expenses was equally sought.
The present invention addresses these and other problems associated with prior mixing systems. The present invention provides both a system and a method for obtaining and maintaining a homogenous slurry in a tank.